Is NI3 Polar or Nonpolar? (And Why?)

NI3 is a POLAR molecule.

But why? 

And how can you say that NI3 is a polar molecule?

Want to know the reason?
Let’s dive into it!

NI3 is a POLAR molecule because the Nitrogen (N) present in the molecule is more electronegative and it has one lone pair, which results in an asymmetric shape of the molecule.
Because of this, the partial positive (ẟ+) and partial negative (ẟ-) charge appears on the molecule. These ẟ+ and ẟ- charges are responsible to make the entire NI3 molecule polar.

Let me explain this in detail with the help of NI3 lewis structure and its 3D geometry.

Why is NI3 a Polar molecule? (Explained in 2 Steps)

To understand the polar nature of NI3 molecule, first of all you should know its lewis structure as well as its molecular geometry.

So let’s see this in the steps below.

Step #1: Draw the lewis structure

Here is a skeleton of NI3 lewis structure and it contains three N-I bonds.

(Note: If you want to know the steps of drawing the NI3 lewis dot structure, then visit this article: NI3 lewis structure, Or you can also watch this short 2 minute video).

So from the above diagram we have come to know that the NI3 molecule has three N-I bonds.

Now in the next step we have to check whether these three N-I bonds are polar or nonpolar.

And we also have to check the molecular geometry of NI3.

Step #2: Check the bond polarity and molecular geometry

The chemical bonds can be either nonpolar, polar or ionic depending on the difference of the electronegativity values (ΔEN) between the two atoms.

Have a look at the above image.

• If the electronegativity difference (ΔEN) is less than 0.4, then the bond is nonpolar covalent bond.
• If the electronegativity difference (ΔEN) is between 0.4 to 1.7, then the bond is polar covalent bond. 
• If the electronegativity difference (ΔEN) is greater than 1.7, then the bond is an ionic bond. ^{[1] [2] [3] [4]}

Now let’s come to the example of NI3 molecule. It has three N-I bonds.

You can see the electronegativity values of Nitrogen (N) and Iodine (I) atoms from the periodic table given below.

From the above image;

• Electronegativity of Nitrogen (N) = 3.04 ^[5]
• Electronegativity of Iodine (I) = 2.66 ^[6]

Now let’s see the polarity of each bond.

For N-I bond;
The electronegativity difference (ΔEN) = 3.16 – 2.66 = 0.5
This value lies between 0.4 to 1.7, which indicates that the bond between Nitrogen (N) and Iodine (I) is polar.
Hence, each N-I bond is a polar covalent bond.

But wait, we also have to look at the molecular geometry of NI3 to know whether it has a symmetric shape or not.

Have a look at this 3D structure of NI3. The Nitrogen atom (N) is at the center and it is surrounded by 3 Iodine atoms (I).

It also has one lone pair on the Nitrogen atom (N).

Due to the lone pair on the nitrogen atom (N), its molecular geometry becomes asymmetric.

Because of this, there are positive and negative poles of charges on the overall molecule of NI3.

Hence, the NI3 molecule is a polar molecule.

I hope you have understood the reason behind the polar nature of NI3 molecule.

See the polarity of other molecules to make your concepts clear:
Is IF3 Polar or Nonpolar?
Is ClF5 Polar or Nonpolar?
Is SCN- Polar or Nonpolar?
Is ICl5 Polar or Nonpolar?
Is CO3 2- Polar or Nonpolar?